Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Carbon dioxide

Brine

Ammonia

2. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

3. A thermostatic expansion valve in a refrigeration system

None of the above

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

4. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-135.8°C

-75.2°C

5. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

6. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Any value

Low

7. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Low boiling point

Good electrical conductor

High risibility with oil

8. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Any one of the above

Equal to unity

Always more than unity

9. The capillary tube, as an expansion device, is used in

All of these

Domestic refrigerators

Water coolers

Room air conditioners

10. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Centrifugal

Miniature sealed unit

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11. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

12. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

Evaporator tubes

13. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

14. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Condenser

Absorber

Evaporator

15. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

16. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

17. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

18. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

19. Which of the following cycles uses air as the refrigerant?

Stirling

Ericson

Bell Coleman

Carnot

20. The boiling point of ammonia is

-30°C

-77.7°C

-10.5°C

-33.3°C

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21. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Compressor and condenser

Evaporator and compressor

Receiver and evaporator

22. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

8 bar

15 bar

2 bar

23. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Collect vapours

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

24. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 3

1: 1

9: 1

25. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

1.33

4.33

2.33

26. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

27. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Zero

Positive

28. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

29. Freon group of refrigerants are

Toxic

Inflammable

Nontoxic and non-inflammable

Non-inflammable and toxic

30. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dry bulb temperature of air

Wet bulb temperature of air

Dew point temperature of air

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31. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

32. Most thermostatic expansion valves are set for a superheat of

10°C

20°C

15°C

5°C

33. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

One heat exchanger

Three heat exchangers

34. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Carnot

Rankine

35. Rating of a domestic refrigerator is of the order of

5 tons

0.1 ton

40 tons

10 tons

36. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

37. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

38. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Normal cooling

Sub-cooling or under-cooling

None of these

39. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant temperature

Takes place at constant entropy

Takes place at constant pressure

40. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.67

0.6

0.4

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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